Method for decimation of images

ABSTRACT

In the case of printing at high addressability, where the cell size is smaller than the spot size, an image can be decimated in a manner that will limit the large accumulation of printed material. The proper decimation of the image will depend on the spot size, the physics of drop coalescence and the addressability during printing. A simple method of using concentric decimation is disclosed herein to enable this process.

This is a divisional application of U.S. patent application Ser. No.11/644,238, filed Dec. 22, 2006, which is hereby incorporated herein byreference in its entirety.

BACKGROUND

The exemplary embodiment relates generally to image processing systemsand, more particularly, to a method of decimating images.

A printed circuit board, or PCB, is a self-contained module ofinterconnected electronic components found in devices ranging fromcommon beepers, or pagers, and radios to sophisticated radar andcomputer systems. The circuits are generally formed by a thin layer ofconducting material deposited, or “printed,” on the surface of aninsulating board known as the substrate. Individual electroniccomponents are placed on the surface of the substrate and soldered tothe interconnecting circuits. Contact fingers along one or more edges ofthe substrate act as connectors to other PCBs or to external electricaldevices such as on-off switches. A printed circuit board may havecircuits that perform a single function, such as a signal amplifier, ormultiple functions.

Two other types of circuit assemblies are related to the printed circuitboard. An integrated circuit, sometimes called an IC or microchip,performs similar functions to a printed circuit board except the ICcontains many more circuits and components that are electrochemically“grown” in place on the surface of a very small chip of silicon. Ahybrid circuit, as the name implies, looks like a printed circuit board,but contains some components that are grown onto the surface of thesubstrate rather than being placed on the surface and soldered.

Ink-jet printing of circuits is an emerging technology that attempts toreduce the costs associated with production by replacing expensivelithographic processes with simple printing operations. By printing apattern directly on a substrate rather than using the delicate andtime-consuming lithography processes used in conventional manufacturing,a printing system can significantly reduce production costs. The printedpattern can either comprise actual features (i.e., elements that will beincorporated into the final circuit, such as the gates and source anddrain regions of thin film transistors, signal lines, opto-electronicdevice components, etc.) or it can be a mask for subsequentsemiconductor or printed circuit board processing (e.g., etch, implant,etc.).

Ink-jet printing of circuits is an emerging technology that attempts toreduce the costs associated with production by replacing expensivelithographic processes with simple printing operations. By printing apattern directly on a substrate rather than using the delicate andtime-consuming lithography processes used in conventional manufacturing,a printing system can significantly reduce production costs. The printedpattern can either comprise actual circuit features (i.e., elements thatwill be incorporated into the final circuit, such as the gates andsource and drain regions of thin film transistors, signal lines,opto-electronic device components, etc.) or it can be a mask forsubsequent semiconductor processing (e.g., etch, implant, etc.).

Several forms of printing etch masks exist. One example is that of aprinted wax pattern used as a copper etch mask for creating PCBs.Another example is laser direct imaging (LDI), a maskless lithographymethod that is currently being used for copper etch masks on PCBs. Ituses a laser to write the raster image of the pattern directly on thephotoresist. In order for it to be to be cost-effective, it is necessaryto have special high speed resists. Also, there is no suitable methodfor soldermask patterning using laser.

Typically, circuit printing involves depositing a print solution(generally an organic material) by raster bitmap along a single axis(the “print travel axis”) across a solid substrate. Print heads, and inparticular, the arrangements of the ejectors incorporated in those printheads, are optimized for printing along this print travel axis. Printingof a pattern takes place in a raster fashion, with the print head making“printing passes” across the substrate as the ejector(s) in the printhead dispense individual droplets of print solution onto the substrate.At the end of each printing pass, the print head makes a perpendicularshift relative to the print travel axis before beginning a new printingpass. The print head continues making printing passes across thesubstrate in this manner until the pattern has been fully printed.

The physical properties of the printed drops on the substrate govern thedrop coalescence and therefore on the quality of the printed features.When a molten drop at temperature T_(o) is ejected from the print headonto the substrate, the solidification time is given by

$\tau_{1} = {\frac{2a^{2}k}{3\alpha \; k_{a}}( {{\ln ( \frac{T_{o} - T_{a}}{T_{f} - T_{a}} )} + {( {1 + \frac{k_{s}}{2k}} )\frac{L}{c( {T_{f} - T_{a}} )}}} )}$

where T_(a) is the ambient temperature, T_(f) is the fusion temperature,α and k are the thermal diffusivity and the thermal conductivity,respectively of the molten drop and k_(s) is the thermal conductivity ofthe substrate, L is the latent heat of fusion and c is the specific heatof the molten drop.

It takes additional time for the drop to cool down to the ambienttemperature and the time scale for this process is given by:

$\tau_{2} = \frac{2.3a^{2}k}{3\alpha \; k_{a}}$

The dynamics of the drop spreading on the substrate is primarilygoverned by the Weber number W_(e) and the Ohnesorge number Z:

$W_{e} = \frac{\rho \; V^{2}a}{\sigma}$$Z = \frac{\mu}{\sqrt{{\rho\sigma}\; a}}$

where μ is viscosity, ρ is density, a is surface tension, V is impactvelocity and a is the radius of the drop.

The Weber number W_(e) scales the driving force for the drop spreadingand the Ohnesorge number Z scales the force that resists the spreading.While impact and capillarity are the main forces for drop spreading,inertia and viscosity are the main factors that resist the dropspreading.

The time scales of the drop spreading and solidification indicate thatthe bulk of the drop solidifies only after the spreading is complete.However, local solidification of the drop occurs prior to the completionof the drop spreading and this determines the shape of the printed drop.The local solidification occurs at the contact line between the drop andthe substrate and arrests further spreading of the drop.

When drops are ejected at a frequency f, the time between subsequentdrops reaching the substrate is

$\tau = \frac{1}{f}$

and the distance between the centers of the subsequent drops on thesubstrate is

$l = {\frac{u}{f}.}$

Drop coalescence between adjacent drops occur when l≦2a and T≦T ₁.

Once dispensed from the ejector(s) of the print head, print solutiondroplets attach themselves to the substrate through a wetting action andproceed to solidify in place. The size and profile of the depositedmaterial is guided by competing processes of solidification and wetting.In the case of printing phase-change materials for etch mask production,solidification occurs when the printed drop loses its thermal energy tothe substrate and reverts to a solid form. In another case, colloidalsuspensions such as organic polymers and suspensions of electronicmaterial in a solvent or carrier are printed and wet to the substrateleaving a printed feature. The thermal conditions and materialproperties of the print solution and substrate, along with the ambientatmospheric conditions, determine the specific rate at which thedeposited print solution transforms from a liquid to a solid.

Photolithography is not an additive process, and so the problem ofprinted material accumulation may not arise even at high addressability.In the case of jet printing, images are typically printed at lowaddressability (˜600 DPI), where large accumulation of the printedmaterial is not a major issue. Even in the case of moderately highaddressability (˜1200 DPI), techniques like halftoning are used.However, this will not give an accurate representation of micro-scalefeatures.

Thus, digital lithography with drop-on-demand technologies is becomingpopular since it is cost-effective for low volume applications. Phasechange materials like wax can be jet printed and used as a masking layerto pattern micro-scale features. Spot placement accuracy is extremelyimportant for semiconductor/PCB fabrication processes. Failure to havegood spot placement accuracy can result in patterning defects, which canreduce the yield and lead to inconsistent device performance. It istherefore necessary to print at high addressability for digitallithography applications so that high spot placement accuracy can beobtained.

When rasterization of the image is done at high addressability and thenprinted, there is a large three-dimensional accumulation of the materialthat is printed, which destroys the features that are obtained. Threedimensional accumulation especially takes place when molten droplets areejected at high addressability onto solidified wax at ambienttemperature. This is very common while printing with multiple passes.

The exemplary embodiment contemplates a new and improved method thatresolves the above-referenced difficulties and others.

INCORPORATION BY REFERENCE

The following references, the disclosures of which are incorporatedherein in their entireties by reference, are mentioned:

U.S. Pat. No. 6,972,261, issued Dec. 6, 2005 to Wong et al., entitled“METHOD FOR FABRICATING FINE FEATURES BY JET-PRINTING AND SURFACETREATMENT,” describes a method of forming smaller features byjet-printing with materials from aqueous or non-aqueous organicsolutions.

U.S. Pat. No. 6,890,050, issued May 10, 2005 to Ready et al., entitled“METHOD FOR THE PRINTING OF HOMOGENEOUS ELECTRONIC MATERIAL WITH AMULTI-EJECTOR PRINT HEAD,” describes a system and method for accuratelyprinting IC patterns and allows the printed features to be optimized foredge profile and electrical continuity.

BRIEF DESCRIPTION

In the case of printing at high addressability, where the cell size issmaller than the printed spot size, an image can be decimated in amanner that will limit the large accumulation of printed material. Theproper decimation of the image will depend on the spot size, the physicsof material coalescence and the addressability during printing. A simplemethod of using concentric decimation is disclosed herein to enable thisprocess.

In one embodiment, a method of decimating an image having one or morefeatures is provided. The method comprises: making an image withconcentric outlines of the features; and applying a masking filter thatdepends on the physical characteristics of the printed material.

In another embodiment, a method of decimating an image having one ormore features is provided. The method comprises: making an image withone or more concentric outer outlines and a halftone inner fill of thefeatures; and applying masking filters for the concentric outlines andhalftone fill based on the physical characteristics of the printedmaterial.

In yet another embodiment, a method of decimating a raster image havingone or more features is provided. The method comprises: skeletonizingthe desired features of the image by M pixels to form an outline;leaving one pixel of the skeletonized outline as black and the innerarea filled as white; and continuing until the entire image is donebased on the radius of the spot size while retaining every N^(th) pixelof the remaining lines and removing the rest.

In yet another embodiment, a method of decimating a raster image havingone or more features is provided. The method comprises: separating thefeatures into outer and inner fill components; skeletonizing the outercomponent of the image by M pixels; leaving one pixel of theskeletonized outline as black and the inner area filled as white andcontinuing until the desired concentric outer outlines are complete;retaining every N^(th) pixel of the concentric outer outlines andremoving the rest; changing the inner fill component to a halftonepattern; combining the concentric outer outlines and halftone innerfill; and separating the image into vertical and horizontal componentsusing a convolution process.

In yet another embodiment, a method of decimating a vector image havingone or more features is provided. The method comprises: contracting thedesired features of the vector image based on desired print cell sizeand spot size, leaving a border vector, and continuing until the entireimage is done; rasterizing the vector image; and retaining every N^(th)pixel of the remaining features and removing the rest, where N is basedon the cell size and the spot size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a printing system suitable for ICprinting;

FIG. 2 illustrates a printed area filled at high addressability showinglarge accumulation of printed material;

FIG. 3 illustrates a printed area filled at 600 DPI showing goodcoverage;

FIG. 4 illustrates an image printed at high addressability withoutappropriate decimation;

FIG. 5 is a block diagram illustrating a desired pattern with fine gaps;

FIG. 6 is a block diagram illustrating spot placement of large dropsnecessary to achieve the appropriate fine gaps shown in FIG. 5;

FIG. 7 illustrates a vector image to be printed;

FIG. 8 illustrates typical 4800 dpi rasterization of the vector image ofFIG. 7;

FIG. 9 illustrates simple decimation of the rasterized image of FIG. 8;

FIG. 10 illustrates the image printed in FIG. 7 with simple decimationat 4800 DPI;

FIG. 11 illustrates a vector image to be printed;

FIG. 12 illustrates typical 4800 dpi rasterization of the vector imageof FIG. 11,

FIG. 13 illustrates simple decimation of the rasterized image of FIG. 12showing uneven feature dimensions;

FIG. 14 illustrates incorrect decimation of the rasterized image of FIG.12 showing uneven fills that can create voids;

FIG. 15 illustrates concentric decimation of the rasterized image ofFIG. 11 showing homogenous feature dimensions and good fill;

FIG. 16 shows concentric decimation of the outer region and halftone forthe inner region of the rasterized image of FIG. 15;

FIG. 17 shows a flowchart of a method of concentric decimation withconcentric outline and concentric inner fill;

FIG. 18 shows a horizontal component convolution mask;

FIG. 19 shows a vertical component convolution mask;

FIG. 20 shows a vertical mask filter;

FIG. 21 shows a horizontal mask filter;

FIG. 22 shows a flowchart of a method of concentric decimation withconcentric outline and halftone inner fill; and

FIG. 23 shows an example of an inner fill halftone filter.

DETAILED DESCRIPTION

Some portions of the detailed description that follows are presented interms of algorithms and symbolic representations of operations on databits performed by conventional computer components, including a centralprocessing unit (CPU), memory storage devices for the CPU, and connecteddisplay devices. These algorithmic descriptions and representations arethe means used by those skilled in the data processing arts to mosteffectively convey the substance of their work to others skilled in theart. An algorithm is generally perceived as a self-consistent sequenceof steps leading to a desired result. The steps are those requiringphysical manipulations of physical quantities. Usually, though notnecessarily, these quantities take the form of electrical or magneticsignals capable of being stored, transferred, combined, compared, andotherwise manipulated. It has proven convenient at times, principallyfor reasons of common usage, to refer to these signals as bits, values,elements, symbols, characters, terms, numbers, or the like.

It should be understood, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The exemplary embodiment also relates to an apparatus for performing theoperations discussed herein. This apparatus may be specially constructedfor the required purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any typeof media suitable for storing electronic instructions, and each coupledto a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the methods described herein. The structure for avariety of these systems will be apparent from the description below. Inaddition, the exemplary embodiment is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the exemplary embodiment as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For instance, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; and electrical,optical, acoustical or other form of propagated signals (e.g., carrierwaves, infrared signals, digital signals, etc.), just to mention a fewexamples.

FIG. 1 is a perspective view of a printing system 100 suitable for ICand PCB printing. Note that while the embodiments disclosed herein aredescribed with respect to IC and PCB printing for explanatory purposes,these embodiments can be applied to any situation in which homogenous,smooth-walled features in a digital lithography pattern is required.

FIG. 1 includes a heat source 104 that heats a reservoir 108 oftypically phase-change material to a temperature that is sufficient tomaintain the material in a liquid state. The system 100 is suitable forcreating a pattern, typically using a printer to controllably ejectindividual droplets to form a patterned protective layer or coating overregions of the substrate to define the outline and fill regions of thedesired feature(s). Regions that were not at one time covered byprotective layer will be subject to deposition (or removal) of materialsused to form various features. Thus, feature size will not be limited bydroplet size, but instead by how closely droplet spots can be positionedtogether without combining to form a joined feature. Generally, thetemperature of the reservoir 108 is maintained above 100 degrees C. andin some embodiments, at temperatures above 140 degrees C., a temperaturesufficient to liquify most phase change organics.

The phase-change material may be an organic media that melts at lowtemperatures. Other desirable characteristics of the phase-changematerial include that the patterning material is non-reactive withorganic and inorganic materials used in typical semiconductor materialsprocessing, and that the phase change material has a high selectivity toetchants. If liquid suspension is used, the substrate material ismaintained above the boiling point of the liquid, and after depositionof the patterning material, the liquid carrier evaporates upon contactwith the substrate surface. When evaporation is used, the phase changeprocess is directed from liquid to vapor, rather than from liquid tosolid.

An additional desirable characteristic of the phase-change patterningmaterial is that the resulting pattern should be robust enough towithstand wet-chemical or dry etching processes. Wax is an example of aphase-change material for both these processes. Kemamide 180-based waxesfrom Xerox Corporation of Stamford Conn. is but one example of asuitable wax for use as a phase-change patterning material.

One or more droplet sources 112 such as a print head receives the liquidphase-change marking material from the reservoir 108 and outputsdroplets 116 for deposition on a substrate 120. Typical substrate 120materials are silicon, glass, and printed circuits boards. The substrate120 is maintained at a temperature such that the droplet cools rapidlyafter deposition. A wetting agent, typically a dielectric material suchas silicon dioxide, SiO₂ or silicon nitride, Si₃N₄, may be included onthe surface to enhance wetting thereby assuring that sufficient wettingoccurs to form a good contact between the pattern and the substrate. Thetemperature of the system is maintained such that the cooling rate issufficient to control the behavior of the droplet after contacting thesubstrate 120 despite the enhanced wetting properties of the surface tobe etched.

When increased coalescence between adjacent printed droplets isrequired, the substrate temperature can be increased to increase dropletspreading and thereby increase coalescence. When printing lines ofKemamide-based wax from an acoustic ink-jet printer, it has been foundthat increasing the substrate temperature from 30 degrees to 40 degreesC. improves the print quality of the pattern. In the case ofKemamide-based waxes, it has been found that excellent results areachieved when the surface is maintained at 40 degrees centigrade, whichis about 20 degrees C. below the freezing point of the wax. At 40degrees C., the temperature of the substrate is still low enough thatthe droplet rapidly “freezes” upon contacting substrate 120.

In order to minimize the possibility of partial midair freezing ofdroplets in the space 121 between the droplet source 112 and thesubstrate 120, an electric field 122 may be applied to accelerate thedroplet from the droplet source 112 to the substrate 120. The electricfield 122 may be generated by applying a voltage, typically between oneto three kilovolts between the droplet source 112 and an electrode orplaten 109 under the substrate 120. For this voltage, the space 121between the print head and the substrate should be held to acorresponding typical range of 0.5-1.0 mm. The electric field 122minimizes droplet transit time through the space 121 and allowssubstrate surface temperature to be the primary factor controlling thephase change operation. Moreover, the increased droplet velocity in thespace 121 improves the directionality of the droplet allowing forimproved straight-line features.

After a droplet of marking material is deposited on the substrate 120,the relative positions of the substrate and the droplet source areadjusted to reposition the droplet source over a second position to bepatterned. The repositioning operation may be achieved either by movingthe droplet source 112 or by moving the substrate 120. A control circuit124 establishes relative motion between the droplet source 112 and thesubstrate 120 in a predetermined pattern. A driver circuit 128 providesenergy to the droplet source 112 causing ejection of droplets when thedroplet source 112 is positioned opposite a region of the substrate 120to be patterned. By coordinating the movement of the droplet source 112with the timing of droplet source outputs, a pattern can be “printed” onthe substrate 120.

As each spot is printed, a feedback system may be used to assure spotsof proper size. An imaging system, such as a camera 130, may be used tomonitor spot size. When smaller features are to be printed, or the spotsize otherwise reduced, a temperature control circuit 123 lowers thetemperature of a surface of the substrate 120. The lower temperatureincreases the quench rate resulting in rapid solidification of the phasechange patterning material upon contact with the substrate 120. Whenlarger spots are needed, usually for merging spots to form largerfeatures, the temperature control circuit 123 raises the temperature ofthe substrate 120. The temperature control circuit 123 may include aheating element thermally coupled to the substrate 120 such that ambientheating of media around the substrate is minimized.

Generally, the phase change material is a solid at temperatures belowapproximately 60 degrees C. As such, it may be unnecessary to cool thesubstrate below room temperature because, as previously described, asufficiently small droplet cools rapidly when a 20 degree temperaturedifferential is maintained between the freezing point of the phasechange material and the substrate temperature. In such cases, thetemperature control circuit may merely be a sensor and a heater thatraises the substrate slightly above room temperature when larger featuresizes are to be printed.

In order to control and align the movement of the droplet source 112,printed alignment marks, such as a mark 113, patterned from a previouspatterned layer may be used to coordinate the next overlying layer. Animage processing system such as the previously described camera may beused to capture the orientation of the previous patterned layer. Aprocessing system then adjusts the position of the overlying patternlayer by altering the pattern image file before actual printing of thepattern layer

Each droplet source may be implemented using a variety of technologiesincluding traditional ink-jet technology and the use of sound waves tocause ejection of droplets of patterning material as done in acousticink printing systems.

To obtain the desired pattern results from the printing system 100, thelayout data must be appropriately processed, the print head 112 must beproperly configured, and the print head 112 must be accurately alignedand calibrated with respect to the substrate 120.

In a typical printing process, the cell size/addressability iscomparable to the spot size, thus resulting in good reproduction of theimages. In the case of semiconductor fabrication processes, good spotplacement accuracy (˜5 um) is desired. In order to obtain this, it isnecessary to print at high addressability (4800 DPI corresponding to ˜5Sum cell size), especially if the print head has unevenly spacedejectors. When the cell size is much smaller than the spot size (e.g.,cell size ˜5 um and spot size ˜50 um), a large accumulation of theprinted material will be observed as shown in FIG. 2. (Some regions inthe figure are out of focus due to the uneven height of the printedmaterial.) Printing at a resolution (DPI) with a cell size correspondingto the spot size should yield the best results, as shown in FIG. 3. Animage printed at high addressability can cause a large build-up ofmaterial such that they are three-dimensional leaning features, as shownin FIG. 4, which may fall at any time.

Corrections to the image must be applied so that the features will bereproduced well when printed at high addressability. It should be notedthat Optical Proximity Correction (OPC) is routinely used in the opticallithography process. OPC is the process of modifying the polygons thatare drawn by the designers to compensate for the non-ideal properties ofthe lithography process. Given the shapes desired on the wafer, the maskis modified to improve the reproduction of the critical geometry. Theaddition of OPC features to the mask layout allows for tighter designrules and significantly improves process reliability and yield. In asimilar manner, digital lithography using jet printing also requiresmaterial coalescence correction in order to reproduce the featuresaccurately. The vertical and horizontal masks that may be used ascorrection to the image depends on the material coalescence, which inturn depends on several physical parameters like the frequency ofprinting, surface tension, viscosity, temperature, etc.

FIG. 5 shows a desired pattern 140 with alternate lines 142, while FIG.6 shows a diagram of printed spots 144 forming a set of alternate lines146 in the rasterized image. Thus, a suitable placement of spots 144 isnecessary to achieve the appropriate fine gaps as shown in FIG. 5. Forexample, in the case of alternate lines of 10 μm width and a spot radiusof ˜40 μm, a 40 μm gap in the rasterized image is necessary forobtaining a 10 μm gap in printed image—even under ideal conditions. Inother words, for a desired gap g, the rasterized image should have a gapof 2*r+c+g, where r is the radius and c is the cell size. A reduction inthe spot size combined with higher addressability is one solution togetting finer gaps with closely spaced fine features

FIG. 7 shows a vector circle, and FIG. 8 shows the same circlerasterized at 4800 DP1. In comparison to this, it can be noted fromFIGS. 9 and 10 that a decimated circle loses the smoothness. This is dueto the fact that only a simple decimation was used. In decimation, a newvalue is calculated from a neighborhood of samples and replaces thesevalues in the minimized image. FIGS. 11, 12, and 13 show a serpentinepattern that is at first a vector image, has then been rasterized andthen finally decimated at 4800 DP1, respectively. Again, the simpledecimation causes uneven feature dimensions and spacing, which are notdesirable. FIG. 14 shows another method of decimation where a simpledecimation is used in the fill area and the outlines are decimated in adifferent fashion. This causes uniform linewidths, but it alsointroduces voids, which are not desirable.

FIG. 15 shows concentric decimation of the rasterized image of FIG. 11with homogeneous line widths and good fill. FIG. 16 shows concentricdecimation of the outer region and halftone for the inner region of therasterized image of FIG. 11. In both cases, skeletonization of the imagewas involved. Briefly, skeletonization of images is a process forreducing foreground regions in an image to a skeletal remnant. Thisremnant largely preserves the extent and connectivity of the originalregion, while discarding most of the original foreground pixels.Skeletonization is typically performed in one of two ways. With oneclass of techniques, a morphological thinning is provided thatsuccessively erodes away pixels from the edges of each ridge line insuch a way that no more thinning is possible and the medial line isleft. What remains approximates the skeleton. With the other class oftechniques, a distance transform of the image is calculated, with theskeleton lying along the singularities in the distance transform. Ineither case, the resulting skeletonized image may be processed to definepoints at which the lines end or bifurcate using methods known in theart.

Concentric decimation of a raster image having one or more features(square, line, circle, etc.) may be accomplished by performing thefollowing basic operations:

-   -   (a) Skeletonize the desired features of the raster image by M        pixels based on the physical characteristics of the printed        material (For example M=([spot radius]/[cell size]));    -   (b) Leave 1 pixel of the skeletonized outline;    -   (c) Continue (a) until the entire image is done; and    -   (d) Retain every Nth pixel of the remaining features and remove        the rest. Again, N is generally equal to M. A smaller number        usually would give better feature edge smoothness, but when it        is very low, accumulation of the printed material occurs and the        features will not be smooth.

Concentric decimation may be accomplished in at least two formats: (1)concentric decimation with concentric outline and concentric inner fill,and (2) concentric decimation with concentric outer outlines andhalftone inner fill. Each of these formats will be explained in greaterdetail below.

We turn now to FIG. 17, where a method (200) of concentric decimationwith concentric outline and concentric inner fill is illustrated.Initially, the cell size (1/[print resolution] in dpi) and the spotradius are determined (202). The entire vector image is then rasterized(204). The features of the image that are to be printed are thenselected (206).

Next, the features are skeletonized by M pixels ([spot radius]/[cellsize]) (208). The integer M may be optimized for smoothness, controllingthe accumulation of printed material, and/or accurate feature dimensionreplication. One pixel of the skeletonized outline is left as black andthe inner area is filled as white (210). The last two steps arecontinued until the entire feature is decimated in a concentric fashion(212). Note that the skeletonization process may vary for differentfeatures of the image and in different regions of the features.

The rasterized image is then separated into horizontal (features below45 degrees) and vertical components (features above 45 degrees) by usingconvolution (214). Convolution consists of the following operations:

-   -   (a) Overlay the appropriate (i.e., horizontal or vertical)        convolution mask on the image;    -   (b) Multiply the coincident terms;    -   (c) Sum all the results; and    -   (d) Move to the next pixel, continuing across the entire        rasterized image.

The convolution equation used to perform (a)-(c) is given by:

$\begin{matrix}{{\sum\limits_{x = {- \infty}}^{+ \infty}{\sum\limits_{y = {- \infty}}^{+ \infty}{{I( {{r - x},{c - y}} )}{M( {x,y} )}}}},} & (1)\end{matrix}$

where M(x,y) is the appropriate convolution mask and l(r,c) is theimage.

An example of a horizontal component convolution mask 150 is shown inFIG. 18, while an example of a vertical component convolution mask 152is shown in FIG. 19. These masks may be also be at different pitches anddifferent angles.

A vertical mask filter 154 (see FIG. 20) is applied for the verticalcomponents to reduce the active pixel pitch (216). As shown in thisexample, every 4^(th) pixel is filled. A horizontal mask filter 156 (seeFIG. 21) is applied for the horizontal components to reduce the activepixel pitch (218). Again, in this example, every 4^(th) pixel is filled.The application of the masking filters may be optimized for smoothness,controlling the accumulation of printed material, and/or accuratefeature dimension replication. Also note that the masking filters mayvary for different features of the image and in different regions of thefeatures.

The horizontal and vertical components are then added to obtain thedecimated outline (220). Finally, some of the closely spaced pixels thatare at the intersection between the horizontal and vertical componentsare removed (222).

We turn now to FIG. 22, where a method (300) of concentric decimationwith concentric outlines and halftone inner fill is illustrated. Onceagain, the cell size (1/[print resolution] in dpi) and the spot radiusmust be determined first (302). The design layer is then rasterized(304). The features of the image that are to be printed are thenselected (306).

Next, the features are skeletonized by M pixels ([spot radius]/[cellsize]) (308). Again, the integer M may be optimized for smoothness,controlling the accumulation of printed material, and/or accuratefeature dimension replication. One pixel of the skeletonized outline isleft as black and the inner area is filled as white (310). The last twosteps are continued until the outer outlines are complete. Note that theskeletonization process may vary for different features of the image andin different regions of the features. The inner fill area is thenseparated (312) and filled with a halftone pattern 158 (see FIG. 23) toobtain the decimated fill (314). The halftone pattern can be atdifferent pitch and at different angles. There may be one or moreconcentric outer outlines with each of them separated by M pixels. Theinner fill area may overlap with the concentric outer outlines to ensuregood coverage.

The skeletonized outline is then separated into horizontal (featuresbelow 45 degrees) and vertical components (features above 45 degrees) asdescribed earlier (316). The vertical mask filter is applied for thevertical components to reduce the active pixel pitch (318). Thehorizontal mask filter is applied for the horizontal components toreduce the active pixel pitch (320). The application of the masks may beoptimized for smoothness, controlling the accumulation of printedmaterial, and/or accurate feature dimension replication. Also note thatthe masking filters may vary for different features of the image and indifferent regions of the features,

The horizontal and vertical components are then added to obtain thedecimated outline (322). The decimated outline and decimated fill areadded (324). Finally, the nearest neighbor pixel and the next nearestneighbor pixel are removed (326).

The methods mentioned so far are raster image processing techniques.Several hybrid combinations of vector and raster image processingmethods may be used to create the concentric decimation. This may beuseful to optimize the speed and memory requirement for the processing.For example, one of the methods would be to rasterize and decimate theboundary vectors. The vector bounded regions may then be contracted,with the rasterization and decimation applied to the new vectors. Theprocess may be continued until the contracted regions are too small torasterize further.

It will be appreciated that several of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A method of decimating an image having one or more features, themethod comprising: making an image with one or more concentric outeroutlines and a halftone inner fill of the features; and applying one ormore masking filters for the concentric outlines and halftone fill basedon the physical characteristics of the printed material.
 2. The methoddefined in claim 1, wherein at least one of the making of an image withthe concentric outlines and the application of the masking filter ismade based on cell size and spot size.
 3. The method defined in claim 1,wherein the making of an image with concentric outlines is optimized forat least one of the following: obtaining edge smoothness, accumulationof printed material, and accurate feature dimension replication.
 4. Themethod defined in claim 1, wherein the application of the masking filteris optimized for at least one of the following: obtaining edgesmoothness, accumulation of printed material, and accurate featuredimension replication.
 5. The method defined in claim 1, wherein themaking of an image with concentric outlines and the masking filter varyfor different features of the image.